A device for the perfusion of cavities with a liquid is already known from German reference 33 38 758 C 2. The pressure sensor used therein reports the actual value of the pressure inside the perfusion line into which the pressure sensor is inserted. A precise measurement of the pressure in the cavity itself cannot be made, because flow losses and hence pressure losses inside the perfusion line and inside the medical instrument distort the measured pressure value.
In order to precisely measure the pressure inside the cavity, the pressure sensor would have to be positioned at a distal end of the medical instrument, in particular an endoscope, such as, for example, an arthroscope. However, this is disadvantageous due to the major mechanical, thermal, and chemical stress on the pressure sensor, particularly during the sterilization of the medical instrument. Also, a miniature pressure sensor becomes necessary with such an arrangement. Such a miniature pressure sensor is relatively expensive. Moreover, a second medical instrument could be inserted only to measure the actual pressure in the cavity. But this would place added stress on the patient and also involve difficulty in handling. Additional sterilization measures would be necessary. Measuring uncertainty would also be very great, because an unnoticed blockage or leakage in the additional medical instrument could considerably distort the pressure measurement.